- The Space Shuttle’s five general-purpose computers, each consisting of a CPU and an I/O Processor (IOP), controlled engines, monitored sensors, displayed data, and navigated the Shuttle.
- The IOP was a separate programmable computer with an unusual multi-threaded architecture, running 25 virtual processors with two different instruction sets (BCE and MSC) to manage network ports and ensure predictable performance.
- The IOP included network interface pages (MIA) that handled analog-to-digital conversion, Manchester encoding, and communication over 24 high-speed data bus networks for reliability and redundancy.
- A PROM page stored microcode in fusible-link PROM chips, which defined the low-level instructions for the IOP’s virtual processors, enabling them to run on a single physical processor.
- The computer system used advanced packaging with ‘pages’—dual-sided circuit boards with flat-pack ICs—and was later upgraded to the AP-101S, combining the CPU and IOP into one unit to save weight and improve performance.
- Key technologies included Manchester encoding for data transmission, hybrid modules for analog circuitry, and a barrel processor design inspired by the CDC 6600 supercomputer.